Modern semiconductor factories use a variety of automation systems for movement of materials and control of fabrication processes. As used herein, the terms semiconductor factory and semiconductor fab are synonymous, and are respectively abbreviated as factory and fab. The various automation systems within the fab include hardware and software that are interfaced to work together to automate the movement of material, data, and control through the fab. Major automation systems in the fab may include: MES (Manufacturing Execution System), AMHS (Automated Material Handling System), MCS (Material Control System), station Control for tool connectivity, EFEMs (Equipment Front-End Modules) and loadports for interface between factory tools and the AMHS, material tracking systems like radiofrequency identifier (RFID) and barcode, and associated software products that may or may not be used in a fab and may or may not be bundled together to handle functions like fault detection, recipe management, scheduling and dispatch, statistical process control (SPC), and others. The AMHS can include sub-systems such as an OHT (overhead hoist transport) system, a near-tool container buffer system, and AGVs (automated guided vehicles). Additionally, the fab can include manually operated material handling and movement systems, such as PGVs (person guided vehicles), among others.
During semiconductor manufacturing, a semiconductor wafer undergoes a plurality of process steps, each of which are performed by a specialized process tool. Workpiece containers are used to convey semiconductor wafers from one tool to another. Each workpiece container is capable of transporting a number of wafers of a specific diameter. The workpiece containers are designed to maintain a protected internal environment to keep the wafers free of contamination, e.g., by particulates in the air outside the workpiece container. Workpiece containers are also known for conveying other types of substrates, such as reticles, liquid crystal panels, rigid magnetic media for hard disk drives, solar cells, etc.
It is an ongoing desire to improve fab logistics and productivity in the areas of cycle time, throughput, WIP (Work-hi-Progress) levels, material handling, etc. Improvement in fab logistics can be of particular concern with regard to fabrication of larger wafers. For example, fabrication of 300 mm and larger wafers requires more automated transport through the fab, thereby benefiting from improved fab logistics. Also, fabrication of smaller technology node devices having decreased line widths may require more process steps, which in turn requires more automated transport through the fab and increases the complexity of cycle time control in the fab. Therefore, improvement in fab logistics can also benefit fabrication of smaller technology node devices.
FIG. 1 shows an example floorplan 101 of a portion of a fab. The floorplan includes a many different fabrication process and/or metrology tools 103A-103L. The fabrication tools can include essentially any type of semiconductor wafer fabrication tool, including but not limited to, wafer plasma processing tools for material etching and/or deposition, wafer cleaning tools, wafer rinsing tools, wafer planarization tools, among others. The floorplan can also include material handling equipment, including but not limited to, lifters/elevators, OHT (overhead hoist transport) systems, OHV's (overhead hoist vehicles), RGV's (rail-guided vehicles), floor conveyers, STC's (material storage/stockers), among others. The floorplan of FIG. 1 shows example travel routes 105 of material handling systems, such as the OHT system, the RGV system, and/or floor conveyers, among others. The floorplan of FIG. 1 also shows a number of material transport vehicles 107, such as OHV's, RGV's, among others, traveling along the various travel routes 105 to move workpiece containers carrying semiconductor wafers or other types of workpieces.
It should be understood that there is an essentially limitless number of floorplan variations possible with a given fab. For example, different fabs can include different combination of process and/or metrology tools. Also, different fabs can include different material handling systems and associated routes. However, what most fabs share is a need to accurately and reliably move workpieces between locations in a most efficient manner as possible. The OHT, RGV, AGV, PGV, and floor conveyer systems, among others, provide a substantial ability to move workpiece containers between locations within a fab. Additionally, the near-tool workpiece container buffering capability provided by the near-tool container buffer system allows for improved management of workpiece container movement and readiness within the fab.
Conventionally, access by the various AMHS sub-systems to certain stations within the fab, such as loadports, has been necessarily restricted to ensure that the various AMHS sub-systems do not collide or interfere with each other in accessing a given station within the fab at a given time. However, while implementation of such access restrictions on the various AMHS sub-systems is effective in avoiding interference conditions within the fab, implementation of such access restrictions on the various AMHS sub-systems can inefficiencies in workpiece container handling within the fab and corresponding reductions in workpiece throughput from the fab. It is within this context of improving AMHS access management that the present invention arises.